Mixed bed ion exchange resin systems for purifying water are well known. The mixed bed of anion and cation exchange resin is typically regenerated from time-to-time, and, according to one conventional process, involves the separation of the anion resin from the cation resin for regeneration treatment. Such a conventional process is disclosed in the U.S. Pat. No. 3,582,504. An inventive modification of that process is disclosed in the U.S. Pat. No. 3,826,761.
Typically, the resins are arranged in a lower cation resin layer and an upper anion resin layer by hydraulic stratification in one process step in a first vessel and by floating one resin in an intermediate-density liquid in a subsequent process step in a second vessel. In each step, the anion resin is withdrawn from the anion resin layer through a pipe communicating with the vessel interior. Although such a procedure is generally satisfactory, not all of the anion resin can be initially withdrawn, and further processing steps may be required. This problem may be more or less significant, depending upon the size of the vessel and upon other parameters.
Accordingly, it would be desirable to provide a method and apparatus for permitting withdrawal of material, such as anion resin, from a vessel in a manner that would substantially eliminate, if not eliminate altogether, the tendency of some material to remain in the vessel. Further, it would be beneficial if such an improved system and apparatus employed relatively simple and inexpensive components.